1. Field of the Invention
The present invention relates to an angular velocity sensor for detecting the angular velocity of a rotating subject.
2. Description of the Related Art
In recent years, angular velocity sensors based on the oscillation gyroscope are used widely in such technical fields as hand tremor detection in video camera, and self-contained driving system in car navigation. In the field of angular velocity sensor itself, automobile driving stability control is a hot field of application, where a highly miniaturized, accurate and reliable angular velocity sensor is in strong demand for use in a vehicle skid prevention system, a vehicle attitude control system for smooth driving on a curved road and so on.
Conventional piezoelectric angular velocity sensors can be classified into two types according to the shape of oscillator, i.e., beam type and fork type. FIGS. 26A and 26B show an angular velocity sensor 800 as a conventional beam type angular velocity sensor. FIG. 26A is a perspective view of the angular velocity sensor 800, whereas FIG. 26B is a sectional view taken along lines B1—B1 in FIG. 26A. The angular velocity sensor 800 includes a beam-shaped or rectangular-parallelepiped oscillator 810, supporting wires 820 for fixing the oscillator to an unillustrated supporting member, a driving piezoelectric element 830, and a pair of detecting piezoelectric elements 840. The oscillator 810 is made of an constant-elasticity metal such as elinvar, and is grounded. The supporting wires 820 are a piano wire for example. The driving piezoelectric element 830 includes a piezoelectric member 831 formed on the oscillator 810, and an electrode 832. The detecting piezoelectric elements 840, each including a piezoelectric member 841 formed on the oscillator 810 and an electrode 842, are disposed on two surfaces which are vertical to the surface provided with the driving piezoelectric element 830. Each of the piezoelectric members 831, 841 is made of piezoelectric ceramic.
When AC voltage is applied to the driving piezoelectric element 830 of the sensor 800, the piezoelectric member 831 expands and shrinks alternately (the reverse piezoelectric effect), causing the oscillator 810 to undergo bending oscillation along the X-axis. Under this condition, if the oscillator 810 is rotated about the Z-axis at an angular velocity of ω, the oscillator 810 comes under the Coriolis force F (F=−2mVω, where m represents the mass of oscillator, and V represents the speed of oscillation) acting along the Y-axis. This causes the oscillator 810 to oscillate also along the Y-axis. In other words, the bending oscillation of the oscillator 810 is now a combined oscillation including an X-axis component and a Y-axis component. The oscillator 810 under the combined oscillation has distortion in its planes vertical to the Y-axis, which is detected on the basis of the piezoelectric effect acting on the piezoelectric members 841 of the detecting piezoelectric elements 840. The piezoelectric elements 840 give an output proportional to the Coriolis force F or the angular velocity ω.
FIG. 27 shows a conventional fork type angular velocity sensor 900. The angular velocity sensor 900 includes a fork-shaped oscillator 910, a driving piezoelectric element 920, and a pair of detecting piezoelectric elements 930. The oscillator 910, made of a constant-elasticity metal such as elinvar, includes a crotch 911 and two arms 912, 913. The arm 912 includes a driving plate 912a and a detecting plate 912b. The arm 913 includes a driving plate 913a and a detecting plate 913b. The driving piezoelectric element 920 is provided in the driving plate 912a of the driving arm 912, and includes a piezoelectric member 921 and an electrode 922. The pair of detecting piezoelectric elements 930, each including a piezoelectric member 931 and an electrode 932, are provided in the detecting plates 912b, 913b. 
In the angular velocity sensor 900 having the above-described construction, when AC voltage is applied to the driving piezoelectric element 920, the arm 912 and the arm 913 oscillate like a tuning fork along the X-axis as indicated by arrows in the Figure. When the oscillator 910 is rotated about the Z-axis at an angular velocity of ω in this condition, the oscillator 910 comes under the Coriolis force F as expressed by the equation given above acting along the Y-axis. This causes the arms 912, 913 to oscillate also along the Y-axis. The arms 912, 913 under the combined oscillation have distortion in their planes perpendicular to the Y-axis. This distortion is detected based on the piezoelectric effect on the piezoelectric elements 930. The output to be obtained is proportional to the Coriolis force F or the angular velocity ω.
However, according to the conventional beam type angular velocity sensor 800, it is necessary to separately make the oscillator 810 and a supporting member (not illustrated) for supporting the oscillator via the wires 820. After the separate fabrication, these two components must be assembled by spot welding, adhesive and so on. Unfavorably, such structural complexity reduces the manufacturing efficiency of the sensor 800. This holds for the conventional fork type angular velocity sensor 900. Specifically, it is difficult to assemble the driving plates 912a˜913a and the detecting plates 912b˜913b into the oscillator 910, as required. Also, it is difficult to form the piezoelectric elements 920, 930 on the oscillator 910 efficiently.
The Japanese Patent Laid-Open No. 2001-116551, for example, discloses a technique, in which a fork type oscillator and a support are made separately, and then bonded together with e.g. an adhesive to assemble an angular velocity sensor. As other examples, the Japanese Patent Laid-Open No. 2000-213940 and the Japanese Patent Laid-Open No. 2001-165664 each discloses an angular velocity sensor including an oscillator made of a piezoelectric material. In these angular velocity sensors, the electrodes are provided in oscillator side surfaces which are perpendicular to each other. This arrangement increases the number of manufacturing steps, as well as making the steps complicated, posing a problem of poor productivity. As another example, the Japanese Patent Laid-Open No. 7-159180 discloses an oscillator formation technique, in which a specific crystal surface of monocrystal silicon is used to perform an anisotropic etching in an inclining direction toward a silicon substrate surface. However, this technique is difficult in controlling the etching, and therefore, has problems in reproducibility and productivity.